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Computational first-principles approach identifies dozens of new platinum-group alloys

7 January 2014

Researchers from Duke University, Brigham Young University, and Carnegie Mellon University have used high-throughput first-principles calculations to identify dozens of platinum-group alloys (binary systems of the platinum-group metals—PGMs—with the transition metals) that were previously unknown but that could prove beneficial in a wide range of applications.

The platinum-group metals (PGMs)—osmium, iridium, ruthenium, rhodium, platinum, and palladium—play essential roles in a wide variety of industrial applications. The primary application of PGMs is in catalysis, where they are core ingredients in the chemical, petroleum, and automotive industries. Although are essential, they are also very costly.

The computations, based on examination of 153 binary PGMs (an incredibly large number from an experimental point of view), predict new stable compounds in 28 binary systems where no compounds have been experimentally discovered (AgPd, CoPd, CuRh, IrNi, IrOs, IrRe, IrRh, IrRu, IrTc, MnOs, MnRu, NiPd, OsRe, OsRh, OsRu, OsTc, PdPt, PdRe, PdTc, PdW, PtRh, PtRu, PtTc, ReRh, ReRu, RhRu, RhTc, and RuTc), and a few dozen of as-yet-unreported compounds in additional systems.

The importance and high cost of PGMs motivate numerous efforts directed at more effective usage or at the development of less-expensive alloy substitutes. Despite these efforts, there are still sizable gaps in the knowledge of the basic properties of PGMs and their alloys; many of the possible alloy compositions have not yet been studied, and there is a considerable difficulty in the application of thermodynamic experiments because they often require high temperatures or pressures and very long equilibration processes.

The possibility of predicting the existence of ordered structures in alloy systems from their starting components is a major challenge of current materials research. Empirical methods use experimental data to construct structure maps and make predictions based on clustering of simple physical parameters. Their usefulness depends on the availability of reliable data over the entire parameter space of components and stoichiometries. Advances in first-principles methods for the calculation of materials properties open the possibility to complement the experimental data by computational results.

… Realizing the potential of first-principles calculations to complement the lacking, or only partial, empirical data requires high-throughput computational screening of large sets of materials, with structures spanning all lattice types and including, in addition, a considerable number of off-lattice structures. Such large-scale screenings can be used to construct low-temperature binary phase diagrams. They provide insight into trends in alloy properties and indicate the possible existence of hitherto unobserved compounds.

… The capability to identify new phases is key to tuning the catalytic properties of PGM alloys and their utilization in new applications, or as reduced-cost or higher-activity substitutes in current applications.

… Given the potential payoff of uncovering such phases, we have undertaken a thorough examination of PGM binary phases with the transition metals, using the first-principles high-throughput (HT) framework AFLOW.

—Hart et al.

The research is part of the Materials Genome Initiative launched by President Barack Obama in 2011. The study appears in the American Physical Society journal Physical Review X and is highlighted in a Viewpoint article in the journal Physics.

We’re looking at the properties of ‘expensium’ and trying to develop ‘cheapium’. We’re trying to automate the discovery of new materials and use our system to go further faster.

—Dr. Stefano Curtarolo, director of Duke’s Center for Materials Genomics

The identification of the new platinum-group compounds hinges on databases and algorithms that Curtarolo and his group have spent years developing. Using theories about how atoms interact to model chemical structures from the ground up, Curtarolo and his group screened thousands of potential materials for high probabilities of stability.

Hart
Top panel: Compound-forming vs. non-compound-forming systems as determined by experiment and computation. Circles indicate agreement between experiment and computation—green for compound-forming systems, gray for non-compound-forming systems. Yellow circles indicate systems reported in experiment to have disordered phases, for which low-energy compounds were found in this work. Red squares mark systems for which low-temperature compounds are found in computation but no compounds are reported in experiment. Bottom panel: The bottom panel ranks systems by their estimated entropic temperature Ts.
Essentially, the top panel, incorporating the computational data, corresponds to what would be observed at low temperatures, assuming thermodynamic equilibrium, whereas a map with only experimental data reports systems as compound Ts for the binary systems in this work. Colors: From red to blue indicates the lowest to highest Ts.
The calculated compound-forming regions, say the researchers, are considerably more extensive than reported by the available experimental data, identifying potential new systems for materials engineering. Hart et al. Click to enlarge.

Now it is up to experimentalists to produce these new materials and discover their physical properties. Previous studies have shown that Curtarolo’s methods are highly accurate in generating recipes for new, stable compounds, but they don’t provide much information about their behaviors.

The compounds that we find are almost always possible to create. However, we don’t always know if they are useful. In other words, there are plenty of needles in the haystack; a few of those needles are gold, but most are worthless iron.

—Stefano Curtarolo

In addition to identifying unknown alloys, the study also provides detailed structural data on known materials. For example, there are indications that some may be structurally unstable at low temperatures. This isn’t readily apparent because creating such materials is difficult, requiring high temperatures or pressures and very long equilibration processes.

We hope providing a list of targets will help identify new compounds much faster and more cheaply. Physically going through these potential combinations just to find the targets would take 200 to 300 graduate students five years. As it is, characterizing the targets we identified should keep the experimentalists busy for 20.

—Stefano Curtarolo

This research was supported by the DOD-ONR (Grants No. N00014-13-1-0635, No. N00014-11-1 0136, and No. N00014-09-1-0921) and the NSF (Grant No. DMR-0908753).

Resources

  • Hart, G.L.W., Curtarolo, S., Massalski, T.B., and Levy, O. (2013) “Comprehensive Search for New Phases and Compounds in Binary Alloy Systems Based on Platinum-Group Metals, Using a Computational First-Principles Approach,” Phys. Rev. X 3, 041035 doi: 10.1103/PhysRevX.3.041035

January 7, 2014 in Catalysts, Materials | Permalink | Comments (0) | TrackBack (0)

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